This invention relates to a gas bag module comprising a gas bag.
Known gas bags have a gas bag wall which has a front wall for the impact of an occupant and a depression starting from the front wall, the depression being formed in that a center portion of the gas bag wall is prevented from a free or any movement during inflation and is restrained. The gas bag has around the depression a ring-shaped chamber to be filled with gas. With such ring-shaped gas bags, the center portion is prevented from moving towards the occupant in that it remains attached to the module. Restraint is effected via the ring-shaped front wall around the depression.
The invention provides a gas bag module in which the depression is closed at least partly, preferably completely. This is achieved in a gas bag module which comprises a gas bag, an outer contour of the gas bag being defined by a gas bag wall which has a front wall for the impact of an occupant and a depression starting from the front wall. The depression is formed in that during inflation of the gas bag a center portion of the gas bag wall is prevented from a free or any movement and is restrained. The gas bag has around the depression a ring-shaped chamber to be filled with gas. At least one limiting strap is provided which engages the gas bag wall at a transition from the front wall to the depression, substantially extends alongside the depression and determines, i.e. defines a depth of the depression. While in gas bags known so far, the depression itself determines the depth of the gas bag, a limiting strap is provided close to the depression in the module proposed, which limiting strap limits the depth of the depression. This means that the portion of the gas bag wall bridged by the limiting strap is longer than the limiting strap itself, so that the limiting strap and not the gas bag wall in the region of the depression determines the depth thereof. The region of the gas bag wall which defines the depression will, however, bulge into the depression in the inflated condition, so that the depression has a smaller opening surface than without a corresponding limiting strap with otherwise identical geometries of the gas bag fabric. The term xe2x80x9ccompletely closedxe2x80x9d should not define that the depression is closed gas tight. Rather, portions of the gas bag wall are pressed against each other so that small openings having a few square millimeter cross area might remain instead of large openings having some square centimer cross area.
Preferably, the gas bag wallxe2x80x94in the region where it defines the depressionxe2x80x94will even bulge to such an extent that portions of the gas bag wall contact each other, preferably opposite portions.
With the invention it is possible that the portions of the gas bag wall contacting each other will rest against each other such that the depression is substantially closed.
This closing of the depression is preferably effected close to the transition from the depression to the front wall, which can be achieved by an appropriate adjustment of the length of the limiting strap to the depth of the gas bag wall which forms the depression.
In accordance with one aspect of the invention, the limiting strap is attached to the front wall or to the region of the gas bag wall that defines the depression.
This attachment can, for instance, be effected as follows: The front wall and the region of the gas bag wall defining the depression preferably consist of fabric layers sewn to each other. At the seam connecting the fabric layers of the front wall and of the depression, the limiting strap is attached to the gas bag, so that with one seam three parts are connected, namely the fabric layers for the front wall and the depression as well as the limiting strap.
In accordance with another embodiment, in which front wall and depression likewise consist of various fabric layers, the fabric layer of the front wall has an opening for forming the transition to the depression. At least one fabric tab of the fabric layer of the front wall protruding into the opening is provided for the attachment of the limiting strap. This embodiment can for instance be realized in that a U-shaped slot is punched into the fabric layer of the front wall, the xe2x80x9cUxe2x80x9d circumscribing the fabric tab.
In accordance with the preferred embodiment, a plurality of limiting straps are provided, which are attached to the front wall and whose points of attachment to the front wall substantially define a plane in the inflated condition of the gas bag. In the inflated condition, the portion of the gas bag wall provided inwards of the points of attachment either lies in the plane or even protrudes from the plane, namely towards the occupant, i.e. opposite to the depression. This means that the gas bag has no funnel-shaped depression in the region of the transition from the front wall to the depression, but the gas bag rather faces the occupant as a planar, closed surface, where some kind of dome may even protrude from the plane.
Closing the depression close to the front wall may even be supported by an expedient cut of the fabric layer defining the front wall. It was found out that a circular opening provides such support less than e.g. a C-shaped, slotted, rectangular, triangular or oval opening. Even a cross-shaped opening or a T-shaped or H-shaped, slotted opening suitably supports closing near the front wall. Surprisingly, these various geometries of the opening are not even a hindrance during deployment of the gas bag. During deployment, the opening must be moved through a ring-shaped outlet opening in the module cover along a stationary middle portion to the outside.
With its end close to the gas bag module, with respect to the inflated condition of the gas bag, the limiting strap is attached to the center portion.